(a) Hybridised orbitals show only head on overlapping and thus form only σ bonds. They never form π bonds. (c) Head on overlapping is stronger than lateral or sideways overlapping. Therefore, the strength of bonds follows the order
πp−p
lateral‌overlapping
<
σs−s<σs−p<σp−p
head on overlapping of same shell
(d) s-orbitals are spherically symmetrical and thus show only head on overlapping and form only σ bonds.